Method of welding



Nov. 7, 1933. s. SCHNETZER METHOD OF WELDING Original Filed June '7,1932 2 vSheets-Sheet 1 Nov. 7, 1 933. 5 SCHNETZER 1,933,937

METHOD OF WELDING Original Filed Jun 7, 1932 2 Sheets-Sheet 2 PatentedNov. 7, 1933 UNITED STATES' PATENT OFFICE METHOD OF WELDING Continuationof application Serial No. 615,924, June '7, 1932. This application March13, 1933.

Serial No. 660,546

8 Claims. (Cl. 219-10) It is the object of my invention to provide ameans, method and apparatus by which a welding apparatus so controlswithin itself the application of welding current according to its needsat various instances during the welding operation so that a perfect weldis secured irrespective of the condition of the electrode tips and thesurface conditions of the work pieces.

Heretofore, attempts have been made in the art to control the variousfactors of current, pressure, time, heat and resistance, as well assurface conditions encountered during the series of welding operations.

My invention is to accept resistance variations as inevitable and toprovide a method of welding and apparatus for practicing the weldingmethod which will automatically accommodate itself to an infinitevariety of resistance conditions which may change within a weldingoperation or within a series of welding operations and give dependably auniform weld no matter what the variations are in conditions. Also, itis my invention to make my apparatus self-controlling by the change ofresistance conditions in the welding circuit at various instances duringa welding operation and during a series of welding operations toautomatically obtain a fusing action through accommodation to thevariations in resistance to such an extent as may be necessary toaccomplish a perfect dependable and uniform weld in a series of weldingoperations.

I thereby eliminate variation in quality and size of the welds whichhave heretofore oc- 35 curred even when produced by accurate setting oftime pressure and current supply.

In particular, it is the object of my invention to apply the weldingcurrent when the decrease of resistance in the control circuit includingthe 4 work pieces has reached a predetermined value so that the weldingcurrent is applied at the predetermined resistance value, the decreasein resistance not being taken for granted as appropriate to thisincrease in pressure.

45 In particular, I provide a control for applying welding current byutilizing a secondary of a transformer of which the work to be welded isa part and in which the work is part of the secondary from whichresistance changes 50 originate.

Upon the accomplishment in this secondary of a predetermined decrease inresistance, which indicates the time and place for the application ofwelding current, I effect through the primary operation a closure of thewelding circuit and thereby apply the welding current to the performanceof the welding. While this decrease in resistance is progressing, theadmittance of the welding current is prevented until the decrease inresistance has reached that predetermined value at which agood weld isproduced.

It is my object to provide for resistance in the secondary including thework as a prime factor and pressure a secondary factor. It is my objectto provide a method of actually employing resistance values as a primefactor in controlling fusing, instead of using pressure as the primefactor. I find that pressure and resistance relations are not dependablyrelated to one another and are susceptible of such serious discrepanciesas to fail to fuse or to overfuse by burning a hole or to make a weld,all with the same settings. I also find that accurate timing of theapplication of the current will likewise fail and not give uniformresults.

In particular, my invention is adapted to nonferrous metals and alloyswhere resistance welding has heretofore not been satisfactory, as, forinstance, in the manufacture of aircraft where such alloys are used andabsolute dependability and uniformity are required.

In particular, it is my object to eliminate the conventional practice ofapplying welding current if a maximum predetermined pressure has beenobtained because uniform pressure will not necessarily result in auniform welding, heating or fusing condition, which is a prerequisite ofa uniform weld under a given value of current and time.

In particular, it is my object to provide a small current which isimposed on the regular primary leads while the welding machine is idlewith welding secondary or electrode tips open.

Upon closing the tips with increased pressure on the work, there willresult an increasing conductance or decreasing resistance andconsequently an increasing consumption of current in the secondary.

Upon the accomplishment of a suflicient current in the secondaryaffecting a relay in a pilot circuit, which operates at predeterminedvalues of current, the relay will then be operated and close the weldingcircuit to apply the welding current at the predetermined resistancevalue between the tips of the electrodes on the work irrespective of thesurface condition of the metal, the time, the pressure, etc.

I, therefore, eliminate the pressure-controlled welder of the prior artwhich has no control over resistance, which is one of the threepredominating factors in resistance welding, such as current, time andresistance.

It is my object to provide a suitable current of low voltage for thepilot circuit.

The effect of leakage is minimized, or prevented,. or made ineffectiveby the application of a suitable pilot current.

For instance, it is the object of my invention to provide a method andapparatus for welding so that, if the spot to be welded happens to havea low resistance due to incidental cleanliness, the welding current willbe started at a low pressure, thus resulting in a regular weld despitethe irregular condition of this particular area before welding, and, ifthe area which is to be welded has a high resistance due to unfavorablesurface conditions, the current will not start until additional pressurehas reduced the resistance to the desired value so as to apply thewelding current to secure a satisfactory weld.

It is my object to provide a method and apparatus of controlling thewelding operation as to current and duration of applying the currentcontrollable by variations in the welding secondary.

To secure perfect welds it is only essential that a predetermined amountof electrical energy be expended in the work pieces in a predeterminedtime, at predetermined contact conditions between the electrode tips andthe surfaces of the Work pieces to be welded. The only variable that Ican accept and the only variable that it is necessary to accept toeliminate all elements due to the human equation, is that due to contactconditions between electrode tips and the surfaces of the work pieces,or, in other words, the electrical resistance in that part of thecircuit between the welding electrode tips.

Referring to the drawings:

Figure 1 shows the parts in position in the circuit where the circuit isidle;

Figure 2 is a similar view showing the parts in welding position withthe welding current being applied;

Figure 3 is a diagram showing a modified form of circuit in at restposition, the circuit including a timer and lock-out device for openingthe circuit upon the completion of the Weld;

Figure 4 is a similar view to Figure 3 showing the state of the circuitduring the welding operation;

Figure 5 is an electrical typical timer circuit;

Referring to the drawings in detail, 1 and 2 indicate the alternatingcurrent power lines. In the line 2 is the welding circuit primarywinding 3 associated with the welding circuit secondary 4 having theelectrodes 5 and 6, between diagram showing a which is engaged the work7. The line 1 has a switch member 8 alternately engaging the terminals 9and 10. This switch member is actuated by the relay 11. The relay 1] isactuated through the wires 12 and 13 of a circuit including thesecondary winding 14 associated with the primary winding 15, suchwindings constituting a relay transformer of the control circuitcomprising the the lines 12 and 13. The primary winding 15 of thistransformer is connected into the lines 16 and 17. The line 18 connectsdirectly from the terminal to the welding circuit primary 3. It will bethus noted that I provide a welding circuit comprising a source ofwelding current and a primary winding and a work circuit comprising theelectrodes, work piece and the secondary of the welding transformer. Thecontrol circuit comprises the relay welding circuit switch and the relaytransformer in the control circuit comprising the secondary of thetransformer, while the primary winding of the relay transformer is incircuit with the welding circuit in idle position.

In operation, upon applying the electrodes 5 and 6 to the work 7 withincreasing pressure and decreasing resistance, the resistance finallydecreases to a point where the work is ready for the application ofwelding current to perform a suitable weld.

Up to this time only negligible current is flowing due to transformerimpedance. The relay transformer comprising the windings 14 and is forthe purpose of transforming current in the circuit to a suitable degree.It shall be understood that the pilot current, active during the controlperiod is to be distinguished from welding current active during theheating period. Current is, therefore, flowing in the idle positionthrough the primary 3 of the welding circuit transformer and makescurrent available at the electrode tips 5 and 6 even though thesecondary welding circuit is still open.

When the electrode tips 5 and 6 are brought together on the work 'I asthe closing movement continues and the parts are pressed togetherthereby closing the secondary welding circuit 4, available current isincreasingly consumed due to the decrease of resistance in the secondarycircuit 4. The control circuit is becoming increasingly energized and,upon being sufiiciently 110 energized at a predetermined value, therelay 11 will operate to move the switch member 8 from the terminal 9 tothe terminal 10 connecting the alternate current lines directly with thewelding transformer so that welding current will pass to the work.

When it is desired to provide a timing mechanism to lock the circuit inwelding position for a predetermined time and then unlock it, I providethe arrangement shown in Figures 3, 4 120 and 5.

It will be understood that the exact form and details of this timer andlock-out device form no part of my invention as I may employ any one ofa number of different types of mechanism for 125 this purpose. Anysuitable instrumentality, such as illustrated, or its equivalent, willdo.

Turning specifically to Figures 3, 4 and 5, I again have the alternatingcurrent lines 1 and 2 terminating at the terminals 19 and 20 which 130are engageable by the switch members 21 and 22 that are actuated by therelay core 23 operating in the relay coil 24 which is connected by wires25 and 26 into a timber 27.

Connected across the supply lines 1 and 2 is a transformer circuitcontrolling the current source designated 28 and 29 containing theprimary 15 and the secondary '14 of a control circuit transformer. Thesecondary 14 is contained in a circuit comprising the lines 12 and 13.These lines terminate at 30 and 31 for engaging the switch arms 21 and22 in open" position of the circuit, that is, in idle position. In theline 13 is a coil 32 having a core 33 operating a switch 34 which restsupon the terminals 35 and 36 of the wires 37 and 38 entering in thetimer 27. Likewise, the wires 28 and 29 are connected by the wires 39and 40 into the timer 27.

Connected across the lines 12 and 13 are the 156 wires 41 and 42 havingthe terminals 43 and 44 which are engaged by the switch member 45 whichis mounted on one end of the core 23 of the relay switch that operatesthe switch members 21 and 22.

In operation, upon the predetermined resistance being accomplished inthe work pieces by the electrodes 5 and 6, the relay 32 is energized,circuit 25 and 26 closed by timer switch 63 (see Figure 5), thusenergizing relay 24 which through 23 switches 21, 22 from the primarycircuit 46 to the supply'lines l and 2 thereby imposing upon thesecondary welding circuit 4 through the electrodes suitable weldingcurrent for performing the welding which continues until the timer andlock-out device operates, as hereinafter described.

In the diagrams as indicated in Figures 3 and 4 the control current istaken from the alternating current power lines 1 and 2 but, under somecircumstances, it may also be taken from another source to avoidinfluences of surges from the welding transformer.

When the current is taken in on the lines 1 and 2 it is transformed intoa suitable amperage voltage ratio leading into the relay 32-33 which isa starting relay.

At this time the current flow through the starting relay is notsufficient to operate it. The control current also passes through themain contactor in control position through the welding transformerprimary 3 and is made available at the electrodes but is of negligiblevalue when the electrodes are open. As the electrodes are pressedtogether, the resistance in the secondary 4 between the tips isdecreased to the desired value.

The double pole switch is actuated and the circuit is closed for theapplication of welding current and is locked in this position for aduration which is predetermined by the timer, 2'7, of which a detaileddiagram is shown in Figure 5. After the welding current has been appliedfor a predetermined time this double pole switch is broken off, lockedout of the welding position and reset into at rest position. Figures 1and 3 indicatethis at rest position. The at rest position is at the sametime the control position, in which the apparatus is again reset for anew operation cycle.

This timer may be any mechanism which controls the duration of the dwellof the welding current breaking the welding current after apredetermined time has elapsed. This may be done manually orautomatically, as set forth in the arrangement in'Figure 5.

My particular invention in this application is directed to starting thewelding current under specific resistance conditions between theelectrodes.

Reclosing of the relay 3233 will not cause a starting of the weldingcurrent but only the opening of relay 32-33 will start the weldingcurrent.

45 and 23 are mechanically so connected that 45 will make contact at theinstant 23, 22 and 21 break from 30 and 31.

Referring to Figure 5 and the timer circuit for opening the circuit atthe end of a Weld, I have provided a timing circuit working upon theprinciple of regulating the opening of the circuit according to thedischarge of a condenser through a fixed resistance which will take agiven time to discharge. If the charge is maintained at the same valueand the value of the resistance increased, a longer time will berequired to discharge the condenser, and vice versa.

Charging of the condenser is accomplished by closing of 34 with 35 and36 as 32 is de-energized, dropping 33 and 34 into contact with 35 and36. 32, 33, 34, 35 and 36 are the component members of the normallyclosed starting relay.

The push rod 62a illustrates the way by which alternating closedpositions of 65 are obtained from movements of 63.

The condenser charge is impressed upon the grid of a tube 60 causing itto be non-conductive dropping out relay 63 and closing the contactor toenergize the welding contactor. The contacts are shunted by a variabledischarge resistor 62 and the discharge takes place until such a pointas the voltage on the condenser 63 is insufiicient to stop the operationof the tube further. At this point the tube 60 will again conductopening 63, breaking circuit 25, causing 19 and 20 to disconnect from 21and 22, thus opening the Welding contactor.

A variable timing is obtained by means of a variable rheostat 62connected to discharge across the condenser. For, instance, a typicalequipment is arranged for a maximum of 1.75 seconds and a minimum ofabout .15 second.

It will be understood that in practice it may be desirable to employseparate sources of current for the timer from that supply to the welderso that the line surges will not cause erratic timing.

This application is a continuation of the application of SiegfriedSchnetzer and Thomas H. Huff, Serial No. 615,924, filed June 7, 1932,which was filed in the names of the joint inventors, Siegfried Schnetzerand Thomas H. Huff, by error and should have been filed as hereinprovided in the name of Siegfried Schnetzer, who

is the sole inventor of the subject matter hereof.

It will be understood that I desire to comprehend within my inventionsuch modifications as may be necessary to adapt it to varying conditionsand uses.

Having thus fully described my invention, what I claim as new and desireto secure by Letters Patent, is:

1. In a method of welding, engaging electrodes with work to be welded,applying to and causing to flow through the electrodes and work a lowstage of current and simultaneously applying a pressure to the workthrough the electrodes until the resistance in the work pieces betweenthe electrodes is decreased to a predetermined value and when that valueis achieved. applying a second higher stage of current to the electrodesand work pieces for welding purposes.

2. In a method of controlling the application of welding current,supplying to and causing to flow through electrodes a low stage ofcurrent and simultaneously applying a pressure ,to the work through theelectrodes, conveying to and applying high voltage welding current tothe electrodes upon the 'decrease of resistance at the welding point toa given value.

3. In a method of controlling the application of Welding current,supplying to and applying to electrodes and work pieces a current lowerthan that for effecting welding, and simultaneously applying a pressureto the work through the electrodes, continuing the application of thiscurrent and pressure to the electrodes and work pieces until apredetermined resistance has been reached and then conveying to andapplying to the electrodes and work pieces a welding current of highvoltage to effect the weld.

4. In a method of starting the application of welding current to workpieces, engaging the work with electrodes, applying to and causing toflow through the electrodes a low voltage primary stage of current,applying a pressure to the electrodes whereby deformation takes placeand resistance through the work is decreased to a predetermined value,and thereupon applying a current of high voltage to the el ctrodes toeffect the weld.

5. In a method of starting the application of a welding current to workpieces, the steps which consist in engaging the Work pieces with theelectrodes and thereby applying pressure thereon, applying a low voltagecurrent to the electrodes and simultaneously therewith applying pressurewhereby deformation takes place and resistance through the work isdecreased, and then applying a current of high voltage to saidelectrodes to effect the weld.

6. In a method of welding, supplying to work pieces in a localized area,current of high and low stages of voltage successively, in the followingsequence, applying the low stage voltage with pressure until apredetermined degree of resistance occurs, and then applying high stagevoltage to effect the weld, thereby controlling the application ofhigher welding current according to the electrical resistance of thework pieces being welded.

'7. In a method of controlling the application of welding current, thesteps which comprise first, engaging the Work with the electrodes, thenapplying a current of reduced voltage and pressure to the electrodes andthrough the work whereby a resulting current lower than welding currentdensity flows through the work, and applying a current of higher voltageto the electrodes when the work pieces reach a predetermined resistance,whereby welding occurs.

8. In a method of applying and controlling the application of weldingcurrent, conveying to and applying to electrodes and work pieces a pilotcurrent, continuing the application of the current until the resistanceof the work pieces is reduced to a given point, and automatically uponthe reduction of such resistance then applying full strength weldingcurrent to the electrodes and work pieces for'final welding.

SIEGFRIED SCHNETZER.

